Identification of Tse8 as a Type VI secretion system toxin from Pseudomonas aeruginosa that targets the bacterial transamidosome to inhibit protein synthesis in prey cells

The Type VI secretion system (T6SS) is a bacterial nanomachine that delivers toxic effectors to kill competitors or subvert some of their key functions. Here, we use transposon directed insertion-site sequencing to identify T6SS toxins associated with the H1-T6SS, one of the three T6SS machines found in Pseudomonas aeruginosa. This approach identified several putative toxin-immunity pairs, including Tse8-Tsi8. Full characterization of this protein pair demonstrated that Tse8 is delivered by the VgrG1a spike complex into prey cells where it targets the transamidosome, a multiprotein complex involved in protein synthesis in bacteria that lack either one, or both, of the asparagine and glutamine transfer RNA synthases. Biochemical characterization of the interactions between Tse8 and the transamidosome components GatA, GatB and GatC suggests that the presence of Tse8 alters the fine-tuned stoichiometry of the transamidosome complex, and in vivo assays demonstrate that Tse8 limits the ability of prey cells to synthesize proteins. These data expand the range of cellular components targeted by the T6SS by identifying a T6SS toxin affecting protein synthesis and validate the use of a transposon directed insertion site sequencing-based global genomics approach to expand the repertoire of T6SS toxins in T6SS-encoding bacteria.

The Pseudomonas aeruginosa T6SS Delivers a Periplasmic Toxin that Disrupts Bacterial Cell Morphology

The type VI secretion system (T6SS) is crucial in interbacterial competition and is a virulence determinant of many Gram-negative bacteria. Several T6SS effectors are covalently fused to secreted T6SS structural components such as the VgrG spike for delivery into target cells. In Pseudomonas aeruginosa, the VgrG2b effector was previously proposed to mediate bacterial internalization into eukaryotic cells. In this work, we find that the VgrG2b C-terminal domain (VgrG2b_C-ter) elicits toxicity in the bacterial periplasm, counteracted by a cognate immunity protein. We resolve the structure of VgrG2b_C-ter and confirm it is a member of the zinc-metallopeptidase family of enzymes. We show that this effector causes membrane blebbing at midcell, which suggests a distinct type of T6SS-mediated growth inhibition through interference with cell division, mimicking the impact of β-lactam antibiotics. Our study introduces a further effector family to the T6SS arsenal and demonstrates that VgrG2b can target both prokaryotic and eukaryotic cells.

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The structure of the VgrG2b C-terminal domain presents a metallopeptidase fold

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VgrG2b exerts antibacterial activity in the periplasmic space

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Toxicity of VgrG2b is counteracted by a cognate periplasmic immunity protein

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VgrG2b_C-ter-intoxicated prey cells bleb at the midcell and lyse

Atomic Structure of Type VI Contractile Sheath from Pseudomonas aeruginosa

Pseudomonas aeruginosa has three type VI secretion systems (T6SSs), H1-, H2-, and H3-T6SS, each belonging to a distinct group. The two T6SS components, TssB/VipA and TssC/VipB, assemble to form tubules that conserve structural/functional homology with tail sheaths of contractile bacteriophages and pyocins. Here, we used cryoelectron microscopy to solve the structure of the H1-T6SS P. aeruginosa TssB1C1 sheath at 3.3 Å resolution. Our structure allowed us to resolve some features of the T6SS sheath that were not resolved in the Vibrio cholerae VipAB and Francisella tularensis IglAB structures. Comparison with sheath structures from other contractile machines, including T4 phage and R-type pyocins, provides a better understanding of how these systems have conserved similar functions/mechanisms despite evolution. We used the P. aeruginosa R2 pyocin as a structural template to build an atomic model of the TssB1C1 sheath in its extended conformation, allowing us to propose a coiled-spring-like mechanism for T6SS sheath contraction.

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We solved a T6SS sheath structure from Pseudomonas aeruginosa (group 3 T6SSⁱ)

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Comparisons between T6SS groups suggest a conserved sheath contraction mechanism

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Extended-state model led to proposal of a spring-like sheath contraction mechanism

TssA forms a gp6-like ring attached to the type VI secretion sheath

The type VI secretion system (T6SS) is a supra‐molecular bacterial complex that resembles phage tails. It is a killing machine which fires toxins into target cells upon contraction of its TssBC sheath. Here, we show that TssA1 is a T6SS component forming dodecameric ring structures whose dimensions match those of the TssBC sheath and which can accommodate the inner Hcp tube. The TssA1 ring complex binds the T6SS sheath and impacts its behaviour in vivo. In the phage, the first disc of the gp18 sheath sits on a baseplate wherein gp6 is a dodecameric ring. We found remarkable sequence and structural similarities between TssA1 and gp6 C‐termini, and propose that TssA1 could be a baseplate component of the T6SS. Furthermore, we identified similarities between TssK1 and gp8, the former interacting with TssA1 while the latter is found in the outer radius of the gp6 ring. These observations, combined with similarities between TssF and gp6N‐terminus or TssG and gp53, lead us to propose a comparative model between the phage baseplate and the T6SS.

Coevolution of the ATPase ClpV, the sheath proteins TssB and TssC, and the accessory protein TagJ/HsiE1 distinguishes type VI secretion classes

The type VI secretion system (T6SS) is a bacterial nanomachine for the transport of effector molecules into prokaryotic and eukaryotic cells. It involves the assembly of a tubular structure composed of TssB and TssC that is similar to the tail sheath of bacteriophages. The sheath contracts to provide the energy needed for effector delivery. The AAA⁺ ATPase ClpV disassembles the contracted sheath, which resets the systems for reassembly of an extended sheath that is ready to fire again. This mechanism is crucial for T6SS function. In Vibrio cholerae, ClpV binds the N terminus of TssC within a hydrophobic groove. In this study, we resolved the crystal structure of the N-terminal domain of Pseudomonas aeruginosa ClpV1 and observed structural alterations in the hydrophobic groove. The modification in the ClpV1 groove is matched by a change in the N terminus of TssC, suggesting the existence of distinct T6SS classes. An accessory T6SS component, TagJ/HsiE, exists predominantly in one of the classes. Using bacterial two-hybrid approaches, we showed that the P. aeruginosa homolog HsiE1 interacts strongly with ClpV1. We then resolved the crystal structure of HsiE1 in complex with the N terminus of HsiB1, a TssB homolog and component of the contractile sheath. Phylogenetic analysis confirmed that these differences distinguish T6SS classes that resulted from a functional co-evolution between TssB, TssC, TagJ/HsiE, and ClpV. The interaction of TagJ/HsiE with the sheath as well as with ClpV suggests an alternative mode of disassembly in which HsiE recruits the ATPase to the sheath.

Ionic composition of PM2.5 at urban sites of northern Greece: secondary inorganic aerosol formation

This study investigates the water-soluble ionic constituents (Na(+), K(+), NH4 (+), Ca(2+), Mg(2+), Cl(-), NO3 (-), SO4 (2-)) associated to PM2.5 particle fraction at two urban sites in the city of Thessaloniki, northern Greece, an urban traffic site (UT) and urban background site (UB). Ionic constituents represent a significant fraction of PM2.5 mass (29.6 at UT and 41.5 % at UB). The contribution of marine aerosol was low (<1.5 %). Secondary inorganic aerosols (SIA) represent a significant fraction of PM2.5 mass contributing to 26.9 ± 12.4 % and 39.2 ± 13.2 % at UT and UB sites, respectively. Nitrate and sulfate are fully neutralized by ammonium under the existing conditions. The ionic constituents were evaluated in relation to their spatial and temporal variation, their gaseous precursors, meteorological conditions, local and long-range transport.

Use of a multiplex polymerase chain reaction system for enhanced bloodstream pathogen detection in thoracic transplantation

BACKGROUND

Bloodstream infections (BSIs) constitute a frequent post-transplant complication in thoracic allograft recipients, especially during the early post-surgical period when patients are under intense immunosuppression. Thus, early and accurate identification of the responsible pathogens is of critical importance for patient survival. In this study we investigated the potential clinical utility of a multiplex real-time polymerase chain reaction (PCR) technology (SeptiFast; Roche Diagnostics) for the detection of BSIs in a cohort of thoracic allograft recipients.

METHODS

Our observational study included analysis of 130 blood samples from 30 thoracic allograft recipients (23 heart and 7 lung) using SeptiFast in parallel with blood culture. Samples were drawn when there were clinical and laboratory signs of BSI. The applied molecular assay has been designed to allow direct detection of a wide panel of Gram-positive and Gram-negative bacteria and fungi in blood samples.

RESULTS

Real-time PCR yielded concurrent negative and positive results with blood culture methodology in 113 (86.9%) and 5 (3.9%) samples, respectively, with 100% concordance in species identification. SeptiFast identified microorganisms in 9 (6.9%) additional samples that were negative by blood culture. The combined use of SeptiFast and blood culture during the early post-transplant period (<2 months) significantly increased the number of positive samples detected to 17.9% (14 of 78) from 7.7% (6 of 78) detected by blood culture alone (p < 0.05). SeptiFast results were available, on average, within 6 hours from sample collection.

CONCLUSIONS

The PCR-based SeptiFast test is a valuable addition to the traditional blood culture method for rapid etiologic diagnosis of BSIs in thoracic transplant recipients, especially during the early post-transplant period.

Sonographic features of intestinal and biliary ascariasis in childhood: case report and review of the literature

Despite the fact that Ascaris lumbricoides is one of the commonest intestinal infections in developing countries, there are very few reports in the literature about the sonographic findings of intestinal and biliary ascariasis in childhood. The clinical manifestations, diagnostic procedures and imaging appearance of intestinal and biliary ascariasis in two patients are discussed with a brief review of the literature.

The HsiB1C1 (TssB-TssC) complex of the Pseudomonas aeruginosa type VI secretion system forms a bacteriophage tail sheathlike structure

Protein secretion systems in Gram-negative bacteria evolved into a variety of molecular nanomachines. They are related to cell envelope complexes, which are involved in assembly of surface appendages or transport of solutes. They are classified as types, the most recent addition being the type VI secretion system (T6SS). The T6SS displays similarities to bacteriophage tail, which drives DNA injection into bacteria. The Hcp protein is related to the T4 bacteriophage tail tube protein gp19, whereas VgrG proteins structurally resemble the gp27/gp5 puncturing device of the phage. The tube and spike of the phage are pushed through the bacterial envelope upon contraction of a tail sheath composed of gp18. In Vibrio cholerae it was proposed that VipA and VipB assemble into a tail sheathlike structure. Here we confirm these previous data by showing that HsiB1 and HsiC1 of the Pseudomonas aeruginosa H1-T6SS assemble into tubules resulting from stacking of cogwheel-like structures showing predominantly 12-fold symmetry. The internal diameter of the cogwheels is ∼100 Å, which is large enough to accommodate an Hcp tube whose external diameter has been reported to be 85 Å. The N-terminal 212 residues of HsiC1 are sufficient to form a stable complex with HsiB1, but the C terminus of HsiC1 is essential for the formation of the tubelike structure. Bioinformatics analysis suggests that HsiC1 displays similarities to gp18-like proteins in its C-terminal region. In conclusion, we provide further structural and mechanistic insights into the T6SS and show that a phage sheathlike structure is likely to be a conserved element across all T6SSs.

Secondary structure and 1H, 13C and 15N resonance assignments of BamE, a component of the outer membrane protein assembly machinery in Escherichia coli

We report the (1)H, (13)C and (15)N backbone and side chain chemical shift assignments and secondary structure of the Escherichia coli protein BamE, a subunit of the BAM (Omp85) complex, the β-barrel assembly machinery present in all Gram-negative bacteria, mitochondria and chloroplasts and is essential for viability.

Orthotopic heart transplantation: ten years' clinical experience

INTRODUCTION

Heart transplantation is the "gold standard" in the treatment of patients with end-stage heart failure who satisfy strict selection criteria.

METHODS

We reviewed ten years' clinical experience (1996-2006) from 53 orthotopic transplants in our centre.

RESULTS

Low perioperative (3.7%) and long-term (7.5%) mortality rates yielded a 95% survival rate in the first year, 92% at five years, and 70% at ten years--significantly better than the corresponding rates worldwide. In addition, excellent functional recovery was achieved in all transplant recipients.

CONCLUSIONS

The strict application of international criteria in the selection of both candidates and donors, together with uninterrupted, multidisciplinary follow up, have made it feasible to perform heart transplantation with excellent results, despite the curiously low number of potential recipients and the shortage of acceptable donor hearts.

The removal of Polycyclic Aromatic Hydrocarbons in the wastewater treatment process: experimental calculations and model predictions

The removal of PAHs during the wastewater treatment process was examined in an activated sludge mode conventional facility. Concentrations reported are taken from an earlier measuring campaign. Removals of PAHs ranged between 28 and 67% in the primary, <1-61% in the secondary stage, and 37-89% in the whole process. Significant positive relationships were observed for removal efficiencies and the log K(ow) of PAHs in the primary and the log K(H) of PAHs in the secondary stage. Experimental removals were compared to those obtained from the FATE model. In the primary stage, predicted removals were lower than those experimentally calculated while in the secondary stage were higher. Predicted removals were apportioned mainly to sorption with negligible contribution from volatilization and biodegradation. Remarkable consistency between experimental and modeled removal efficiencies (-20-+20%) was observed for almost all PAHs in the whole treatment process.

Endovascular repair as first-choice treatment of iliac pseudoaneurysms following renal transplantation

Pseudoaneurysms of the arterial anastomosis are rare complications of renal transplantation. We report three cases of patients with extrarenal pseudoaneurysms and describe their treatment by endovascular placement of covered stents. Two of these aneurysms were due to vascular infections by fungi. An 8-week antifungal therapy proved to be successful in preventing the risk of fungal infection of the graft material in both patients. All three of our grafts remained open 2 months to 3 years after their placement with no evidence of stenosis or infection.

Profile analysis of ambient and source emitted particle-bound polycyclic aromatic hydrocarbons from three sites in northern Greece

Polycyclic aromatic hydrocarbons (PAHs) adsorbed to ambient PM(10) were determined at three sites in Thessaloniki, northern Greece, during the period June 1997-July 1998. Ambient PAH profiles exhibited significant seasonal and spatial variations. Source PAH profiles were obtained for a number of urban, industrial and geological sources including cement, fertilizer and asphalt production, quarry operations, metal electroplating, metal welding and tempering, steel manufacture, lead and bronze smelters, metal scrap incineration, oil burning, non-catalyst equipped passenger cars, diesel fueled taxies and buses, paved road dust and soil dust. Principal component analysis (PCA) and diagnostic ratios were employed to compare ambient and source PAH profiles in an attempt to recognize compositional patterns. Similarities between the ambient PAH profiles and the profiles of certain sources, such as vehicular emissions, oil burning and metal industries, were identified.

Chronic gastric volvulus and hypertrophic pyloric stenosis in an infant

Chronic secondary mesenteroaxial gastric volvulus associated with hypertrophic pyloric stenosis has rarely been mentioned in the general medical literature. We report the case of a 2-month-old boy whose clinical symptoms, which included distension of the stomach and projectile vomiting, suggested the diagnosis of hypertrophic pyloric stenosis but who was later diagnosed with chronic secondary mesenteroaxial gastric volvulus. Sonographic examination revealed findings consistent with a rotated stomach, and subsequent plain chest radiography demonstrated a left diaphragmatic eventration. An upper gastrointestinal series radiographic examination with barium contrast enhancement confirmed the diagnosis of mesenteroaxial gastric volvulus. Surgery was performed, and the boy recovered well. A follow-up sonographic examination performed 3 months post-operatively revealed no abnormalities. This case demonstrates that primary or secondary gastric volvulus, although rare in children, should be considered in the differential diagnosis of pediatric patients with a history of vomiting.

Polycyclic aromatic hydrocarbons in the bulk precipitation and surface waters of Northern Greece

Bulk (wet and dry) precipitation and surface water sampling was undertaken in the main plain of central Macedonia in Northern Greece. Fourteen polycyclic aromatic hydrocarbons (PAHs) included in the US EPA's priority pollutant list were analysed. The concentrations determined in bulk precipitation were in general within the range of values worldwide reported. Concentrations were highest in the cold months. Deposition fluxes of PAHs were of the same order of magnitude as reported data. The greatest values were found when high concentrations of PAHs in precipitation coincided with large precipitation amounts. The concentrations of PAHs in surface waters (main rivers, tributaries, ditches, etc) were in general lower than those in bulk precipitation, and among the lowest reported for European rivers, excepting Np and Ph. Bulk deposition and domestic effluents are suggested as being the main PAH sources into surface waters.

Polycyclic aromatic hydrocarbons in the ambient air of Greek towns in relation to other atmospheric pollutants

Polycyclic aromatic hydrocarbons (PAHs) were determined in the ambient air of six towns in N. Greece. This paper presents the variability of the particle-bound PAHs concentrations and the particle PAH content during the cold and the warm months. Correlations of total PAHs with other atmospheric pollutants were largely different among towns indicating that the relative contribution of emission sources is different in each location. In the warm months PAHs were significantly correlated with vehicular pollutants thus suggesting traffic as the major PAH emmitting source. The same was also deduced from the comparison of the ambient PAH profiles to the profiles of particular sources. The contribution of residential heating was significant in most towns during winter. Principal component analysis of the data did not result in a clear distinction between towns thus suggesting that all are influenced by similar source types. Finally, the risk associated with the inhallation of carcinogenic PAHs in each town was estimated and compared to the risk from more urbanized/industrialized sites in N. Greece.

Bioconcentration of polycyclic aromatic hydrocarbons in vegetables grown in an industrial area

The polycyclic aromatic hydrocarbon (PAH) content was determined in the inner tissue of various vegetable species and their growing environment (soil and atmosphere) in the greater industrial area of Thessaloniki, northern Greece. The lower molecular weight compounds dominated in both vegetable leaves and roots. Statistical analysis of variance showed that species and season are the factors that significantly affect PAH concentrations in inner vegetable tissue and soil, respectively. Principal component analysis indicated that the mixture of PAHs in inner vegetable tissue was very similar to that in air vapour thus suggesting gaseous deposition as the principal pathway for the accumulation of PAHs. Soil-to-vegetation and air-to-vegetation bioconcentration factors were calculated and their relationships with PAHs' physicochemical properties were investigated. Solubility and the octanol-water partition coefficient, as well as vapour pressure and the octanol-air partition coefficient were proved to be good predictors for the accumulation of PAHs in inner root and leaf tissue, respectively.